Hydrogen elimination and thermal energy generation in water-activated chemical heaters

ABSTRACT

A hydrogen suppressing, flameless, heat generating chemical composition including magnesium or a magnesium-containing alloy, a hydrogen suppressor or eliminator, particulate carbon, a metallic salt including a cation and an anion and water. The anion is selected from the group consisting of silicate, carbonate, bicarbonate, phosphate, borate, perborate, percarbonate, perphosphate, persulfate, nitrate, nitrite, ferrate, permanganate, and stannate and combinations thereof. The magnesium or magnesium-containing alloy, hydrogen suppressor or eliminator, particulate carbon, metallic salt and water are each present in a proportional amount to generate sufficient heat to heat water, medical supplies and/or consumable rations.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation-in-Part of application Ser. No.12/322,596, filed on Feb. 4, 2009, which is a Continuation-in-Part ofapplication Ser. No. 12/069,995, filed on Feb. 14, 2008, which is aContinuation-in-Part of application Ser. No. 11/657,852, filed on Jan.25, 2007, which claims the benefit of Provisional Application Ser. No.60/764,213, filed on Feb. 1, 2006, which applications are incorporatedherein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

The U.S. Government has a paid-up license in this invention and theright in limited circumstances to require the patent owner to licenseothers on reasonable terms as provided for by the terms of Contract Nos.W911QY-06-C-0021, W911QY-07-P-0335 and W911QY-08-C-0096 awarded by theDepartment of Defense.

BACKGROUND OF THE INVENTION

Flameless Chemical Heaters (FCH), also known as Flameless Ration Heaters(FRH), are used in Meal, Ready-to-Eat (MRE) packaging to provide hotmeals to soldiers in the field or for warming or heating medicalsupplies or food rations in confined spaces (e.g., tents, underwatershelters) or in remote locations where there is no heat source. TheseFCHs or FRHs are generally based on the reaction of magnesium with waterto form magnesium hydroxide and hydrogen which releases about 85 kcal ofenergy per mole of magnesium. Equation [1] below sets forth thisreaction.

Mg+2H₂O→Mg(OH)₂+H₂+Δ  [1]

There are two types of MREs. The first is an individual meal for thesoldier. The second one is a family-style meal for a group of 10-20soldiers, called the Unitized Group Ration-Express (UGR-E). Both ofthese MREs use a Flameless Ration Heater (FRH) as the heat source forthe hot meal. The temperature of a 250 gram individual MRE entrée can beraised by 100° F. in about 10 minutes using a 14 g FRH. Typically, theprocess of heating food consists of adding about 40 ml of water to theFRH by the military or other user, in order to activate the chemicalreaction that produces the heat. Presently, the FRH consists of amagnesium, iron and salt mixture. The iron is used to activate thereaction of magnesium with water, whereas the salt prevents theformation of a magnesium oxide film on the magnesium metal surface. Thereaction products are magnesium hydroxide and hydrogen. With theindividual MRE, the liberation of up to 13 liters of hydrogen gas hasnot been a substantial safety problem.

The Unitized Group Ration-Express (UGR-E) is a complete meal in a boxand can feed small groups of eighteen soldiers. Again, the food isheated by using a proportionally larger FRH that is activated by theaddition or distribution of water. The problem associated with therelease of hydrogen is significantly magnified with group meals. For aUGR-E weighing 28 pounds and requiring approximately 400 g of heatermaterial, the amount of hydrogen released is typically 13.5 cubic feetor 380 liters. Thus, the concern is that generation of this largequantity of hydrogen in a confined space will exceed the Lower ExplosiveLimit of 4%.

Accordingly, there is a need for an improved system for the elimination,or at least minimization of hydrogen generation in magnesium/water basedflameless heaters.

SUMMARY OF THE INVENTION

It is therefore a principal object of the invention to eliminate orsuppress the cogeneration of hydrogen in all types of magnesium-basedFCHs, to prevent the release of hydrogen into the atmosphere andpreventing potentially explosive situations by means of a novel process.

Thus, one principal aspect of the invention includes useful methods forgenerating energy for flameless heating, such as for foodstuffs, water,medical supplies, etc., especially in the case of outdoor applicationsfor camping, emergency, military applications all without thecogeneration of hazardous hydrogen by the steps of:

(i) forming a reaction mixture including magnesium ormagnesium-containing alloy, a hydrogen eliminator or suppressor andparticulate carbon; and,

(ii) adding a metallic salt and water to the reaction mixture, themetallic salt includes a cation and an anion and the anion is selectedfrom the group consisting of silicate, carbonate, bicarbonate,phosphate, borate, perborate, percarbonate, perphosphate, persulfate,nitrate, nitrite, ferrate, permanganate, and stannate and combinationsthereof.

The metallic salt and water are added either sequentially or togetherand the reaction mixture, metallic salt and water in combinationgenerate sufficient thermal energy for heating an article or substancewhile simultaneously eliminating or suppressing the generation ofhydrogen. Thus, the metallic salt may be added to the reaction mixtureprior to the addition of water, the water may be added to the reactionmixture prior to the addition of the metallic salt, the metallic saltand water may be added to the reaction mixture simultaneously or themetallic salt and water may form a solution which is in turn added tothe reaction mixture.

This inventor discovered a new class of useful hydrogen suppressors oreliminators for flameless heaters.

Accordingly, it is still a further principal object of the invention toprovide novel methods and compositions of matter for the flamelessgeneration of thermal energy, including heater devices and meal,ready-to-eat packaged meals wherein the methods and compositions notonly suppress or eliminate the cogeneration of potentially hazardoushydrogen, but surprisingly, were discovered to provide a substantiallyaccelerated temperature rise for more prompt heating of the packagedmeal compared to other state-of-the-art flameless chemical heaters.

Generally, for purposes of this invention the expression “hydrogensuppressor” as appearing in the specification and claims is intended tomean any metal-containing oxidizing agent that is suitable for at leastminimizing, and more preferably, eliminating the cogeneration ofhydrogen in the presence of magnesium or a magnesium-containing alloy.The metal of the metal-containing oxidizing agent, more specifically, isone having multiple valences, and includes as a preferred group, oxidesof transition metals, such as manganese and/or oxides of ruthenium, andmore particularly, manganese dioxide and ruthenium dioxide, to name buta few.

It should be understood, there are other representative examples ofreactants in addition to oxides of manganese and ruthenium as hydrogensuppressors or eliminators, which when mixed with magnesium and reactedwith water at least minimize, and more preferably totally suppress thecogeneration of hydrogen, while effectively generating the desiredthermal energy. Generally, the useful hydrogen suppressors oreliminators are transition metal oxides that avoid the cogeneration ofhydrogen in the reaction with magnesium or magnesium alloys.Representative examples include noble metals, such as platinum, iridiumand rhodium. Other multivalent transition metal oxides include suchmembers as iron, cobalt, nickel, silver, gold, tin, zirconium, hafnium,tantalum, lead, copper, and so on.

Useful magnesium-containing alloys for the above reaction mixture canalso include at least one alloying element, such as iron, cobalt,nickel, zinc, aluminum and mixtures thereof.

The subject invention also contemplates optional additives in practicingthe flameless heating methods disclosed herein comprising at least onemember selected from hydrogen overvoltage suppressors, promoters,flowing agents and reaction activators.

The subject invention also contemplates the addition of a combination ofmetallic salts to the composition of step (i). For example, the metallicsalt added to the composition of step (i) may include a plurality ofunique metallic salts. Such compositions including a plurality ofmetallic salts are within the spirit and scope of the claimed invention.

As previously mentioned, it is still a further principal object of theinvention to provide novel hydrogen suppressing or eliminatingflameless, thermal energy generating chemical compositions. Thecompositions comprise reaction mixtures having at least: magnesium or amagnesium-containing alloy; a hydrogen suppressor or eliminator;particulate carbon; a metallic salt including a cation and an anion,wherein the anion is selected from the group consisting of silicate,carbonate, bicarbonate, phosphate, borate, perborate, percarbonate,perphosphate, persulfate, nitrate, nitrite, ferrate, permanganate, andstannate and combinations thereof; and, water. Moreover, in someembodiments, the cation is selected from the group consisting of analkaline metal and an alkali metal, while in other embodiments, thecation is selected from the group consisting of calcium, magnesium andpotassium.

Generally, the reactants are present in proportional amounts sufficientto generate heat for promptly raising the temperature of substances,products or articles, such as water, medical supplies, consumablerations, and the like, to the desired temperature within a reasonabletime period. As previously pointed out, it was surprisingly andunexpectedly discovered the novel hydrogen suppressor or eliminatorcompositions of the present invention provide a substantiallyaccelerated temperature rise over known flameless heat generatingcompositions comprising magnesium and water. Moreover, it was alsosurprisingly and unexpectedly discovered that the introduction of ametallic salt of the present invention provides more desirable heaterperformance characteristics, i.e., rate of heating and amount ofhydrogen generation.

As previously mentioned, the hydrogen suppressing or eliminatingflameless heat generating compositions may have other optionalreactants, such as a hydrogen overvoltage suppressors, reactionpromoters, flowing agents and reaction activators.

In addition to magnesium metal, the hydrogen suppressing, flameless heatgenerating reaction mixtures may also be prepared from alloys ofmagnesium, prepared from alloying metals, such as iron, cobalt, nickel,zinc, aluminum and mixtures of the same. Such alloys are known amongskilled artisans, and are commercially available through ordinarychannels of commerce.

Besides magnesium, the flameless heat generating reaction mixtures, likethe previously described methods, also comprise at least one hydrogeneliminator/suppressor, such as oxides of manganese and/or ruthenium, andmore particularly, manganese dioxide and/or ruthenium dioxide in asufficient amount to suppress the generation of hydrogen. This includesother transition metal oxides like those previously discussed inconnection with the methods of the invention.

It is yet a further principal object of the invention to provide forheater devices, such as trays and pouches comprising the hydrogensuppressing, flameless, heat generating compositions, particularly forheating water, food rations, including medical supplies especiallyuseful for camping and military applications. This is especiallyintended to include Meal, Ready-to-Eat military ration packagingcomprising the above flameless heater devices.

BRIEF DESCRIPTION OF THE DRAWING

For a further understanding of the invention and its characterizingfeatures reference should now be made to the accompanying drawingswherein:

FIG. 1 is a top plan view of a porous sealed packet of flameless heatgenerating composition of the invention with a portion of the poroussealed cloth removed to show the milled composition;

FIG. 2 is a partial isometric view of a flameless heater containmentpouch with a portion of the front panel removed for an interior view ofthe pouch with the porous packet of heat generating powder and the foodration packet;

FIG. 3 is similar to that of FIG. 2, except the containment pouch hasbeen placed in a containment box, and water is being introduced into theflameless heater containment pouch for initiating the generation of heatfor heating the food packet in the pouch;

FIG. 4 is a side elevational view of the containment box with a sidewallof the box removed to show the arrangement of the flameless heater pouchwith sealed food ration packet in the pouch like that of FIG. 3, andwith water added, wherein the box is propped up at the open end toassure the water remains in contact with the porous packet of heatgenerating powder;

FIG. 5 is a plot illustrating the rate of temperature rise of aflameless heat generating composition relative to the rate oftemperature rise of a known composition;

FIG. 6 is a further plot of the rate of temperature rise of anotherflameless heat generating composition relative to the rate oftemperature rise of a known composition;

FIG. 7 is a further plot of the rate of temperature rise of additionalflameless heat generating compositions relative to the rate oftemperature rise of a known composition;

FIG. 8 is a further plot of the rate of temperature rise of yet anotherflameless heat generating composition relative to the rate oftemperature rise of a known composition;

FIG. 9 is a further plot of the rate of temperature rise of threedifferent chemical heater compositions each activated using a water andNaCl solution;

FIG. 10 is a diagram of an apparatus arranged to measure the generationof hydrogen by chemical heater compositions;

FIG. 11 is a plot of the rate of temperature rise of an embodiment ofthe flameless heat generating composition of the present inventionrelative to the rate of temperature rise of a known composition; and,

FIG. 12 is a further plot of the rate of temperature rise of anotherembodiment of the flameless heat generating composition of the presentinvention relative to the rate of temperature rise of three other heatgenerating compositions.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention relates to novel methods and reactionmixtures/compositions for the generation of flameless heat mainlywithout the co-generation of potentially hazardous hydrogen previouslyassociated with prior art methods and compositions. The methods of theinvention employ at least one transition metal oxide powder, such as anoxide of manganese and/or ruthenium, for example, mixed with powderedmagnesium or magnesium-containing alloy to generate flameless heat, freeof, or with minimal cogeneration of hydrogen. The methods of the presentinvention can in part be demonstrated by the following representativereaction scheme set forth in Equation [2]:

Mg°+2MnO₂+H₂O→Mn₂O₃+Mg(OH)₂+Δ  [2]

It should be appreciated that thermodynamically, Equations [1] and [2]are sanctioned to proceed and generate the same amount of heat when thereactants are mixed in proportions dictated by the stoichiometry. Thus,the amount of heat generated by 1 gram of Mg via Equation [1] is thesame as 5.37 grams of the reactants via Equation [2].

The reaction according to Equation [2] eliminates or suppresses hydrogengeneration, or at least minimizes its cogeneration, while providingaccelerated temperature rise over prior methods, i.e., more spontaneousheat generation than the known Mg+H₂O reaction of Equation [1], as willbe demonstrated by the methods below currently used in flamelesschemical heaters or flameless ration heaters. It may be noted that theaddition of CuCl₂, NaNO₃, and trichloroacetic acid to magnesium werebelieved to eliminate the hydrogen evolution reaction. However, NaNO₃and trichloroacetic acid are not effective in fully suppressing hydrogengeneration, and CuCl₂ in the MREs is not acceptable because ofenvironmental and health considerations.

The novel chemical compositions of the present invention react andgenerate sufficient heat for promptly heating water, medical supplies,consumable rations, and the like, without simultaneously generatinghydrogen. Methods of the invention rely on a metallic element, e.g.,magnesium or alloy thereof, a hydrogen suppressor or eliminator, ametallic salt and water, the latter of which acts as a reactant and amedium for the reaction. Generally, the hydrogen suppressor oreliminator is a transition metal oxide, and include inter-alia noble andnon-noble metal oxides. Other useful representative oxides include PtO,IrO₂, RhO₂, Fe₂O₃, Co₃O₄, NiO, Ag₂O, Au₂O₃, CuO, TiO₂, ZrO₂, HfO₂, Ta₂O₅and PbO₂.

Optional additives for the hydrogen suppressing flameless heatgenerating chemical compositions and methods may include a hydrogenovervoltage suppressor, a promoter, flowing agent, activators, and thelike.

The metallic element in the chemical composition that generates heat ismagnesium or magnesium alloy containing from about 0.001% to about 10%iron, cobalt, nickel, zinc, aluminum, either singly or in combinationwith each other. A preferred composition is pure or substantially puremagnesium with small or trace amounts of other metals, e.g., <0.001% toabout 0.1% of the alloying elements, iron, cobalt, nickel, zinc andaluminum. One preferred hydrogen suppressor in the chemical compositionis MnO₂ and RuO₂. A preferred hydrogen suppressor may be either γ-MnO₂or β-MnO₂, both known oxides, made either electrolytically or chemicallyby known methods, or from a naturally occurring ore that is treated. Theamount of MnO₂ in the chemical composition is in ranges from about 1 toabout 10 times the stoichiometric amount required for the Mg+MnO₂reaction with water, the preferred amount being 1-10 times thestoichiometry.

The hydrogen overvoltage suppressor in the chemical composition may be ametal sulfide, the metal preferably being Fe, Co, Ni, or a highlyelectrically conductive carbon, present in amounts ranging from about0.001 to about 1%. The promoter in the chemical composition ispreferably a carbon in particulate or powder form, present in an amountranging from about 0.001 to about 20 percent-by-weight. The filler orflowing agent includes such representative members as silicon dioxideand calcium carbonate, and is present in an amount ranging from about0.001 to about 10 percent-by-weight. They are effective in alsopromoting the reaction rate of the flameless heater reaction mixtures.Activators for the reaction mixtures include alkali metal halides, suchas NaCl, magnesium halide salts, such as MgCl₂, MgBr₂, includingMg(ClO₄)₂, and so on. Additionally, activators for the reaction mixturesinclude thermally and electrically conducting, high surface areasynthetic graphite and other conducting carbon materials. An example ofa suitable synthetic graphite includes Asbury 4827, produced by AsburyGraphite Mills, Inc., of Asbury, N.J., while suitable conducting carbonsinclude Asbury TC 307, also produced by Asbury Graphite Mills, Inc.,KETJENBLACK® (such as EC600JD), produced by Akzo Nobel Polymer ChemicalsLLC, of Chicago, Ill., BLACK PEARLS® 2000 or 1300, both produced byCabot Corporation, Alpharetta, Ga. The amount of activator can vary inthe range from about 0.001 to about 50%. One preferred activator isMgCl₂, the other being electrically conductive carbon.

The reaction scheme set forth supra is an electrochemical corrosionreaction, the anodic reaction being the oxidation of Mg to form Mg²⁺ions, the cathodic reaction being the reduction of MnO₂ to Mn₂O₃ and theelectron transfer processes proceeding on the surface of MnO₂. It is forthis reason that there is no need for a conducting electrolyte, such asa salt solution, to activate the reaction described supra. However, Mgis prone to form MgO and therefore, the reaction described supra doesnot proceed to completion unless an electrically conducting materialsuch as carbon is added to the Mg/MnO₂ mixture and blended thoroughly toestablish/provide good electrical connectivity between MnO₂ and Mgsites.

MgCl₂ serves the same purpose but in a different way. Thermodynamicpotential-pH diagrams for an Mg/water system at various temperaturesshow that the pH at which Mg²⁺ is in equilibrium with Mg(OH)₂ shifts tolower pH values as the temperature increases. Thus, when MgCl₂ is added,the temperature rises to as high as 120-150° C., and facilitates thesolubility of Mg(OH)₂ at pH=7, which is the pH of the water added to thereactants. Note that at pH=7 and at 25° C., the stable species is Mg²⁻,whereas at pH=7 and at 90° C., there is an equilibrium between these twospecies. This is the reason why addition of MgCl₂ promotes theaccessibility of the blocked MgO sites. The pH value at which Mg²⁺ is inequilibrium with Mg(OH)₂ is strongly dependent on the activity of Mg²⁺ions in the solution. It has been found that the higher the activity,the lower the pH value. We generally added MgCl₂ corresponding to anactivity of >>1.

It will be understood, activators, e.g., MgCl₂ and carbon, may beintroduced into the flameless heater compositions of the invention byvarious methods. For example, one method provides for blending/mixing anactivator, such as MgCl₂ and/or carbon in particulate form into themilled magnesium and hydrogen suppressor or eliminator when preparingthe reaction mixture, before introducing the water reactant.Alternatively, an aqueous solution of the MgCl₂, e.g., 5 to 7 M solutionof the activator in the water reactant (45 to 60 wt % solution), can beprepared and introduced together as a salt solution into the milled Mgand hydrogen suppressor or eliminator reaction mixture. However, theformer method of blending the activator with the milled Mg and hydrogensuppressor or eliminator is generally more preferred because it is moreeffective in suppressing hydrogen than the latter method. Moreover, theaddition of the metallic salt of the present invention may occur in thesame fashion as the introduction of the activators. For example, themetallic salt may be either milled with the Mg and hydrogen suppressor,or alternatively, may be used to form an aqueous solution which is lateradded to the Mg and hydrogen suppressor mixture. Still further, themetallic salt may be incorporated via either means as a pure metallicsalt, or alternatively, a plurality of suitable metallic salts incombination.

Example 1

In order to demonstrate the details of the invention based on aMg/MnO₂+H₂O system according to the equation [2] above, the followingexperiment was conducted.

A 99.98% pure Mg metal sample of 500μ particle size from Superior MetalPowders, Franklin, Pa., was used in this test, and contained traceamounts, i.e., 85 ppm Al, 4 ppm Cu, 300 ppm Fe, 250 ppm Mn, 50 ppm Na,150 ppm Si, 100 ppm Zn and 50 ppm Ca. In addition, a 300μ size γ-MnO₂powder from Tronox, LLC, Henderson, N.V., was used with a purity of 99%.The γ-MnO₂ contained trace amounts, i.e., 8600 ppm S, 2600 ppm Ca, <100ppm Mg, <1000 ppm Al, <100 ppm Si, <100 ppm Cl, 700 ppm K, <1000 ppm Crand <100 Sn ppm.

The above Mg and γ-MnO₂ powders were used to make a batch sample in astoichiometric ratio according to equation [2], above. Approximately 500g of the 300μ particle size MnO₂ and 69.44 g of 500μMg were combined andplaced in a mill. In this case the mill was a Vibrokinetic Energy (VKE)Mill, from Microgrinding System, Inc., Little Rock, Ark., model 624(diameter=6″ and tube length=24″). This mill was operated with 36stainless steel rods (6 with a diameter=1″, 30 with a diameter= 7/16″)with a length of 24″. The sample mixture was introduced into the millvia a 2″ diameter feed. All the screws and openings were tightened andsecured prior to running the mill for 6 hours. At the end of the 6 hourmilling period, the sample remained in the mill over night to cool. Thesample was removed with a Nalgene scoop, transferred to a 600 mlstainless steel beaker and stored in a desiccator with calcium sulfateas the dehydrating agent.

Following FIG. 1 of the drawings, polypropylene bag 10 was fabricatedfrom porous filter cloth 12 (Unilayer 270), available from MidwestFiltration Company, Cincinnati, Ohio. The filter cloth was a 6-ply sonicbonded polypropylene laminate having a thickness of 22 mils (0.5588 mm),a weight of 91.6 g/m², an air permeability of polypropylene 635 l/m²/secand a Mullen Burst strength of 80 psi. The porous filter clothfabricated from polymeric fibers allows the transmission of water, andthe release of gases while precluding the blockage of pores by the solidreactants and/or products owing to its depth loading characteristics. An8″×11″ sheet of the filter cloth was used to fabricate bag 10 forcontainment of milled Mg/MnO₂ reaction mixture 20 supra. It should beappreciated that as described infra bag 10 may be constructed in avariety of ways. For example, filter cloth 12 may be constructed from asingle layer of 6-ply sonic bonded polypropylene laminate as shown inFIG. 1, or filter cloth 12 may be a dual layer bag consisting of twodifferent filter cloth materials such as polyester fibers for one layerand polypropylene fibers for another layer, and either layer may be theinner or the outer layer of bag 10. Additionally, filter cloth 12 may beconstructed from multiple layers of polyester fibers, e.g., four to sixlayers, or may be constructed as a dual composite fabric consisting ofan inner layer of spunbond/meltblown/spunbond filter media containing100% polypropylene and an outer layer of a 3-ply bonded polypropylenefiber cloth. An example of such an inner layer is Unipro 260-SMS whichis made of white spunbond/meltblown/spunbond filter media containing100% polypropylene with a thickness of 19 mils (0.4826 mm) and a weightof 2.60 oz/yd² (91.96 g/m²), with an air permeability of 17.1 cfm/ft²(86.9 l/m²/sec) and a Mullen Burst of 71 psi. It should further beappreciated that the foregoing examples are within the spirit and scopeof the claimed invention.

First, filter cloth 12 was cut into a 6″×8″ sheet. The filter cloth wasthen made hydrophilic. One of two procedures and surfactants may be usedin making the porous filter cloth hydrophilic. One method employs a “dipand nip” technique. This method requires taking the porous hydrophobiccloth and dipping it into a 5% aqueous solution of surfactant. Theexcess surfactant is then squeezed off by passing the cloth through apair of nip rollers. The second method provides for applying a dab ofPluronic-25R2 surfactant, from BASF Corp., Florham Park, N.J., on one orboth sides of the cloth.

Hydrophilic porous filter cloth 12 was then fabricated into bag 10 byfolding the treated 6″×8″ sheet in half. The bottom 4″ of side 14 and 6″of side 16 were heat sea form the pocket or bag 10 with opening 22 onthe top 4″ of side 18 left open to allow for filling before applying thefinal heat seal. The heat seals were made using a Uline 8″ impulseSealer (H-163). 100 g of the milled and dried Mg/MnO₂ powder 20described supra was then placed in the Unilayer 270 polypropylene bag 10and opening 22 on the top sealed closed. This sealed flameless rationheater reaction mixture bag 10 was then placed in green non-porous“poly” bag 24 (FIG. 2) having bottom closure seal 26 and upper opening28. Poly bag 24, fabricated with a polypropylene film, had a capacitysufficient for also holding 250 g of water as “water test pouch” 30 usedas a surrogate for a regular food ration packet. Poly bag 24 containingthe reaction mixture bag 10 and water test pouch 30 were placed in“chipboard box” 34 (FIG. 3).

60 ml of water 31 (FIG. 3) were then added to green poly bag 24 on thesame side as the ration heater and the top of bag 24 was folded over(not shown). The green poly bag, and its contents in “chipboard box” 34(FIG. 4) were held substantially horizontally with the rationheater/reaction mixture bag 10 below water test pouch 30. After 30seconds, the system was set at a slight incline (FIG. 4), to preventwater loss, and allowed to react for 30 minutes. The temperaturevariation was recorded as a function of time and shown in FIG. 5, andlabeled 50.

Example 2

In order to compare the performance of the hydrogen suppressing,flameless heat generating composition prepared according to Example 1, asecond sample of the known flameless heat generating compositioncomprising Mg and H₂O only was prepared.

8 g of 500μ Mg/Fe, from Innotech Products, Inc., Cincinnati, Ohio aspresently used in a U.S. Army ration heater, was prepared according tothe recipe in U.S. Pat. No. 5,611,329. This sample was placed in a“non-woven” bag material from Innotech Product, Inc. The Innotech bagmaterial was a roll configured into four, 1″ compartments distributedthrough the length of the roll. 6″ of this material was cut from theroll and the bottom was heat sealed with a Uline, 8″ impulse sealer(H-163). Each of the four compartments was filled with 2 g of the Mg/Feand the ration heater was heat sealed closed (not shown).

The completed flameless ration heater was placed in a green polyethylenebag, from the U.S. Army, with a 250 g water pouch. After thirty seconds,40 ml of an aqueous solution of 0.25 M sodium chloride was pouredbetween the water pouch and the flameless ration heater. The top of thegreen bag was folded over and the green bag with its contents was placedin a “chipboard” box (not shown). For approximately 30 seconds, the boxsystem was held horizontally with the ration heater at the bottom. Then,the system was set at a slight incline to prevent water loss, andallowed to react for 30 minutes. The temperature variation was recordedas a function of time and shown in FIG. 5, labeled 52.

FIG. 5, which plots test pouch temperature relative to time (minutes),demonstrates a significantly faster and higher (steeper) heat elevationtemperature occurring with the flameless heating Mg/Mn oxide reactionmixture prepared according to Example 1 relative to the known flamelessheater composition of the prior art employing Mg/Fe reaction mixturewithout transition metal oxide (Example 2).

Example 2A

100 g of 500μ Mg/Fe, from Innotech Products, Inc., Cincinnati, Ohio, aspresently used in a U.S. Army ration heater, was prepared according tothe recipe set forth in U.S. Pat. No. 5,611,329. This sample was placedin an 8″×11″ bag made from the “non-woven” bag material from InnotechProduct, Inc., that was configured into four, 2″ compartmentsdistributed through the length of the roll. Each of the fourcompartments was filled with 25 g of 500μ Mg/Fe and the ration heaterwas heat sealed closed.

This completed ration heater was placed in a UGR-E heating tray, overwhich a 3500 g “water pouch” was placed. This assembly was placed in acard board box and then 330 ml of 1.5% NaCl solution was added. The cardboard box was then closed and the edges sealed with a tape. Thetemperature variation was recorded as a function of time over a 60 mperiod, and shown in FIGS. 7 and 8, labeled 54.

Example 3

In order to demonstrate a further embodiment of a chemical heatercomposition which includes a metal halide activator, a furtherexperiment was performed with the reactants: Mg+MnO₂+MgCl₂ by means ofthe following protocol.

The milling procedure for the Mg/MnO₂ mixture was the same as thatstated in Example 1. 45 g of the milled Mg/MnO₂ mixture was mixed with15 g of 325 mesh MgCl₂, from Sigma-Aldrich, Inc., St. Louis, Mo. ThisMg/MnO₂/MgCl₂ mixture was placed in a dual layer bag consisting of twodifferent filter cloth materials made of polyester fibers (Finon C305NW)and polypropylene fibers (Unilayer 270). Finon C305NW is made ofpolyester fibers with a thickness of 7 mils (0.1778 mm) and a weight of50.9 g/m², with an air permeability of 1,778 l/m²/sec and a Mullen Burstof 50 psi. This dual layer configuration is essential with Mg/MnO₂/MgCl₂mixtures to provide thermal stability to the bag via the polyesterfabric and the depth loading characteristic via the polypropylene,6-ply, Unilayer. Both of the bag materials from Midwest Filtration werereceived in 8″×11″ sheets and cut into 6″×8″ sheets. To make thesematerials hydrophilic, the “dip and nip” process of Example 1 wasemployed. To configure the pouch, the Finon polyester material wasplaced aside the smooth surface of the Unilayer polypropylene and bothare folded in half to make a 4″×6″ pouch with the polyester inside theUnilayer polypropylene (not shown). A Uline 8″ impulse Sealer (H-163)was used to heat seal the two materials together. The 6″ side, parallelto the fold and one of the 4″ sides were sealed prior to adding thereaction mixture. An additional seal, parallel to the 6″ side and downthe center of the pouch was also added to make the pouch into twocompartments. 30 g of the Mg/MnO₂/MgCl₂ mixture was added to each of thecompartments. The pouch was heat sealed closed and placed in a green“polybag” with a 250 g water test pouch as a surrogate for a ration. 40ml of water was added to the green bag on the same side as the rationheater. The top of the bag was folded over and the whole system wasplaced in a “chipboard” box. For approximately 30 sec, the box was heldhorizontally with the ration heater under the water pouch. Then thepouch was set at a slight incline for thirty minutes, as in Example 1.The temperature variation was recorded as a function of time and shownin FIG. 6, and labeled 56.

The performance of the FRH composition of the Example 3 was also testedrelative to the Example 2 with the results demonstrated by FIG. 6 of thedrawings.

FIG. 6 illustrating the performance of the FRH composition (Example 3)comprising Mg and MnO₂, plus MgCl₂ activator also provided asignificantly faster and higher (steeper) rise in the generation ofthermal energy relative to the known flameless heater composition of theprior art employing Mg/Fe reaction mixture without transition metaloxide (Example 2).

Bag Materials

As described above, bag 10 may be constructed in a variety of ways. Asset forth in Example 1, bag 10 may be fabricated from porous filtercloth, such as Unilayer 270. In this example, the filter cloth is a6-ply sonic bonded polypropylene laminate. Additionally, as set forth inExample 3, a dual layer bag consisting of two different filter clothmaterials may be fabricated from polyester fibers, such as Finon C305NW,and polypropylene fibers, such as Unilayer 270. Furthermore, it has beenfound that bag 10 may also be fabricated from multiple layers, e.g.,four to six layers, of polyester fibers, such as Finon C305NW. Similarto the previously described fabrications, the multiple layers can besonically bonded and made hydrophilic by the “dip and nip” process ofExample 1. Each of these fabrications provides varying levels of thermalstability and depth loading capability so that fine particles areprevented from blocking the pores and preventing entry of water fromoutside to the reactants inside the bag material. In the dual layerconfiguration, the polyester fiber provides thermal stability to the bagwhile the polypropylene provides the depth loading characteristic.Moreover, porous filter cloth fabricated from polymeric fibers allowsthe transmission of water, and the release of gases while precluding theblockage of pores by the solid reactants and/or products owing to itsdepth loading characteristics.

It has been found that with when Unilayer-based ration heater pouchesare used in combination with the present invention, a very small seepageof carbon and/or MnO₂ fines occurs before and after the reaction. Suchleakage leads to an unappealing aesthetic appearance of the heater andstains the hands of the person handling the heater. It has been foundthat these issues may be eliminated by employing a dual composite fabricconsisting of an inner layer of 1.5 oz, Unipro 260-SMS(spunbond/meltblown/spunbond filter media containing 100%polypropylene), and an outer layer of Unilayer 135 which is a 3-plybonded polypropylene fiber cloth. The temperature-time profiles of thepresent invention in combination with the Unilayer 270 and the Unilayer135/Unipro-SMS arrangements described above are shown in FIG. 7 andlabeled 58 (Unilayer 270) and 60 (Unilayer 135+Unipro-SMS),respectively. The foregoing examples depicted in FIG. 7 are shown withan UGR-E heater, and the test procedure is set forth in Example 20below. A prior art example is also shown in FIG. 7 and labeled 54. Ithas been found that use of the above described Unilayer 135/Unipro260-SMS fabric not only improved the heating rate, but also effectivelyprecluded leakage of carbon and/or MnO₂ fines.

Hydrogen Generation

The amount of hydrogen generated by the FRH reaction mixtures ofExamples 1, 3 and 20 was measured on a comparative basis with the FRHreaction mixture of the prior art (Example 2) by collecting off-gasesand analyzing for hydrogen content by means of gas chromatography. Theresults are provided in Table 1 below:

TABLE 1 Example Solid Reactants Liquid Reactants Hydrogen Suppression 1Mg/MnO₂ Water   99%  2* Mg/Fe Water + NaCl**   0% 3 Mg/MnO₂/MgCl₂ Water  94% 20  Mg/MnO₂/C Water 97.1% 99.7%  20*** Mg/MnO₂/C Water + NaCl98.9% *Results same as Mg/Fe/NaCl (0.6 g) + Water **Water containing 40g H₂O + 0.6 g NaCl ***Same composition as Example 20, however liquidreactant is water having 1.5% NaCl

Example 4

The following example demonstrates the method for removing residualmoisture (3.3% H₂O ) from electrolytic manganese dioxide to near zerolevel for improving useful shelf-life of the reaction mixture.

In performing the process, 500 g of MnO₂ is placed in an oven set to400° C. for 2 hours and then heated at 110° C. for 24 hours. This MnO₂sample is mixed with Mg powder and milled following the proceduredisclosed in Example 1. The remaining steps of the process correspond tothose disclosed in Example 1, containing Mg+MnO₂.

Example 5

The following example demonstrates the method for removing residualmoisture (3.3% H₂O ) from electrolytic MnO₂ to near zero level inpreparing a reaction mixture comprising Mg and MnO₂ (water-free), plusMgCl₂ activator for improving useful shelf-life of the reaction mixture.

In performing the process, 500 g of MnO₂ is placed in an oven set to400° C. for 2 hours and then heated at 110° C. for 24 hours. This MnO₂sample is then mixed with Mg powder and milled following the procedurein Example 1. The remaining steps of the process are the same as thosedisclosed in Example 3, containing Mg+MnO₂+MgCl₂.

Example 6

The following example was performed to demonstrate the procedure forpreparing a homogeneous reaction mixture that maximizes electricalcontact of all the MnO₂ with Mg in the reaction mixture.

In performing the process, 300 g of 60μ γ-MnO₂, from Tronox, LLC, wasmixed with the Mg powder and milled according to the procedure inExample 1. The remaining process steps corresponded to those disclosedin Example 1.

Example 7

The following example was performed to demonstrate the procedureemployed in preparing a reaction mixture comprising Mg+MgCl₂ with smallparticle size (60μ) MnO_(2.)

In performing the process, 300 g of 60μ γ-MnO₂, from Tronox, LLC, wasmixed with Mg powder and milled following the procedure in Example 3.The remaining steps are the same as that described in Example 3.

Example 8

The following example demonstrates preparation of a reaction mixtureaccording to present invention comprising magnesium with manganesedioxide except with very small average particle size of 0.8μ.

In performing the process, 300 g of 0.8μ MnO₂ available from SigmaAldrich can be mixed with Mg powder and milled following the procedurein Example 1, above. The remaining steps of the process can follow thosedisclosed in best mode Example 1.

Example 9

The following example also demonstrates preparation of a flamelessheater reaction mixture according to the present invention, but withultra fine particulates of MnO₂ (0.8μ γ-MnO₂) hydrogen suppressant, plusMgCl₂ activator.

In preparing the reaction mixture, 300 g of 0.8μ MnO₂, from SigmaAldrich, is mixed with Mg powder and milled following the procedure ofExample 3, above. The remaining steps for preparation of the reactionmixture correspond to those also described in best mode Example 3.

Example 10

The following best mode example also demonstrates a further aspect ofthe invention except the improved flameless heater composition isprepared with two (2) times the stoichiometric amount of manganesedioxide.

In preparing the composition, 600 g of MnO₂ from Tronox, LLC, is mixedwith Mg particles and milled as described in working Example 1, supra.The remaining steps correspond to those also described in Example 1.

Example 11

The following best mode example also demonstrates a further aspect ofthe invention for preparing flameless heater compositions prepared withtwo (2) times the stoichiometric amount of manganese dioxide incombination with magnesium chloride activator.

In preparing the reaction mixture/composition, 600 g of MnO₂ fromTronox, LLC, is mixed with the Mg particles and milled in Example 1. Theremaining steps correspond to those also described in Example 3.

Example 12

The following example demonstrates a further alternative embodiment ofthe invention comprising for Mg+MnO₂+1% Zn° metal, wherein an additionalalloying metal, i.e., zinc, is introduced into the composition to formsurface alloyed magnesium metal particulates during the milling step.

In preparing the reaction mixture/composition, 500 g of 300μ MnO₂ (sameas the MnO₂ disclosed in Example 1, procedure for Mg+MnO₂), 69.44 g of500μ Mg (same as the Mg° described in Example 1 procedure for Mg+MnO₂)and 5 g Zn° particles, from Sigma Aldrich with a purity of 99.99%, werecombined, placed in the VKE mill and milled for 6 hours. The remainingprocedure is the same as that described in Example 1, procedure forMg°+MnO₂.

This inventor found that the milling process is effective for: (i)mixing the ingredients to form a homogeneous reactive composition; (ii)assures desired intimate electrical contact between the ingredients,i.e., Mg+MnO₂+Zn° metal; (iii) is an effective means of forming surfacesalloyed with added metals, such as zinc, cobalt, nickel, iron, aluminumand mixtures of the same; and, (iv) also promotes better surfaceadhesion of the MnO₂ to the magnesium or alloyed magnesium.

Example 13

This example discloses a flameless heating composition of the inventioncomprising a combination of both oxides of manganese and ruthenium in a30% RuO₂, 70% MnO₂ proportional range.

In preparing the composition, 48.61 g of 500μ Mg (same as disclosed inExample 1), 350 g of 300μ particle size of MnO₂ (same as the MnO₂disclosed in Example 1 procedure for Mg+MnO₂) and 150 g RuO₂, 99.99%pure from Sigma Aldrich (12036-10-1), were combined, placed in the VKEmill and milled for 6 hours. The remaining procedure is the same as thatdescribed in Example 1.

Example 14

This example discloses a flameless heating composition of the inventionsimilar to Example 13, except the combination of oxides of manganese andruthenium have been reversed wherein RuO₂ is present in 70% range, andthe MnO₂ is present in a proportional range of 30%.

In preparing the composition, 20.83 g of 500μ Mg (same Mg disclosed inExample 1 and the procedure for milling Mg+MnO₂), 150 g of 300μ of MnO₂(same MnO₂ disclosed in Example 1 and milling procedure for Mg+MnO₂ inExample 1) Mg, and 350 g RuO₂ (same as the RuO₂ described in Example 13,Mg+30% RuO₂+70% MnO₂), were combined, placed in the VKE mill and milledfor 6 hours. The remaining procedure is the same as that disclosed inExample 1.

Example 15

This best mode example demonstrates a flameless heating composition ofthe invention comprising RuO₂ as the sole hydrogen suppressing agent.

In preparing the composition, 45.50 g of 500μ Mg (same as the Mgdisclosed in Example 1) and 500 g RuO₂, (same as the RuO₂ disclosed inExample 13), were combined, placed in the VKE mill and milled for 6hours. The remaining procedure is the same as that described in Example1.

Example 16

This example demonstrates a further embodiment of the invention whereinthe flameless heater mixture includes in addition to Mg and MnO₂, 10%by-weight carbon to promote the rate of reaction and the generation ofheat.

In preparing the reaction mixture/composition, 69.44 g of 500μ Mg (Sametype of Mg disclosed in Example 1), 500 g MnO₂ (same as the MnO₂disclosed in Example 1) and 50 g carbon from Cabot Corp., Boston, Mass.,available under the trademark Vulcan XC72R, Lot: GP-3860 were combinedand placed in the VKE mill and milled for 6 hours. The remainingprocedure for this composition follows the same protocols as disclosedin Example 1, above.

Example 17

A further embodiment of the invention is presented wherein 1% Na₂S isintroduced into the flameless heater composition Mg+MnO₂ composition asa hydrogen overvoltage suppressor. A metal sulfide may be incorporatedinto the composition as a fail safe in the event hydrogen isunexpectedly generated.

The flameless heater composition was prepared by mixing 69.44 g of 500μMg (same Mg disclosed in Example 1), 500 g of MnO₂ (same MnO₂ disclosedin Example 1) and 5 g Na₂S (from Sigma Aldrich), and placing the mixturein the VKE mill and milling for 6 hours. The remaining procedurecorresponds to that described in Example 1, above.

Example 18

Another embodiment of the flameless heater compositions of the inventionincludes the introduction of a filler/flowing agent, such as 2% SiO₂ tothe magnesium/manganese dioxide.

This embodiment may be prepared by combining 69.44 g of 500μ Mg (thesame Mg disclosed in Example 1) with 500 g MnO₂ (the same MnO₂ disclosedin Example 1) and 10 g of 20μ0 SiO₂ (from Sigma Aldrich, purity=99.5%)and placing the mixture in the VKE mill and milling for 6 hours. Theremaining procedure for preparing corresponds to that disclosed inExample 1.

Example 19

A similar flameless heater composition to that of Example 18 may beprepared using 2% CaCO₃ filler/flowing agent with the magnesium andmanganese dioxide.

The reaction mixture/composition may be prepared by combining 69.44 g of500μ Mg (same Mg as disclosed in Example 1), 500 g MnO₂ (same MnO₂ asdisclosed in Example 1) and 10 g of 20μ CaCO₃ (from Sigma Aldrich,purity=99.0%), and placing the mixture in the VKE mill and milling for 6hours. The remaining procedure corresponds to that described in Example1.

Example 20

A 99.98% pure magnesium powder of 200-300μ particle size from SuperiorMetal Powders and containing 60 ppm Al, 50 ppm Cu, 300 ppm Fe, 700 ppmMn, 50 ppm Si, 50 ppm Zn and 80 ppm Sn was used in this test. The 70-80μγ-MnO₂, from Tronox, LLC, with a purity of 99% and contained 1.2% 50₄²⁻, 2600 ppm Na, 190 ppm Al, 310 ppm C, 35 ppm Fe and 400 ppm K. Thesetwo materials were used to make a batch sample, in a stoichiometricratio according to Equation [1] above, along with 5% Asbury 4827 carbon,a synthetic graphite of <20-<30μ particle size, containing 1440 ppm Al,865 ppm Ca, 2150 ppm Fe, 300 ppm Mg, 200 ppm Na and 2900 ppm Si.

Approximately 1100 g of a mixture containing 919.2 g MnO₂, 52.2 g C and130 g Mg was weighed and placed in the Vibrokinetic Energy (VKE) Mill,from Microgrinding System, Inc., model 624 (diameter=6″ and tubelength=24″). This mill is run with 36 stainless steel rods (6 with adiameter=1″, 30 with a diameter= 7/16″) with a length of 24″ as astainless steel rod. The sample mixture is loaded into the mill via the2″ diameter feed. All screws and openings are tightened and securedprior to running the mill for 1.5 hours. At the end of 1.5 hours, thesample is left in the mill for 20 minutes to cool. The sample is removedwith a Nalgene scoop, transferred to a 1000 ml stainless steel beakerand stored in a desiccator with calcium sulfate as the dehydratingagent.

A Unilayer 270 bag material from Midwest Filtration is used to containthe milled Mg/MnO₂ mixture. First, the bag material is cut into a16.5″×11″ sheet and folded in half to make a 8.25″×11″ bag. Prior toadding the sample, one of the 8.25″ sides and the 11″ side is heatsealed to form a pocket. The task is done with a Uline, 8″, ImpulseSealer (H-163). 450 g of the milled Mg/MnO₂ mixture is placed in theUnilayer Pocket and sealed closed. This completed ration heater isplaced in a UGR-E tray, over which the 3500 g “water pouch” is placed.This assembly is placed in a card board box and then 350 ml of water isadded. The card board box is then closed and the edges sealed with atape. The temperature variation was recorded as a function of time overa 60 minute period, and is presented in FIG. 8. The results of themixture of this Example is labeled 62, while the results of a prior artmixture is labeled 54.

The reaction set forth in Equation [2] above suppresses hydrogen;however, it does not proceed to provide as much heat as the compositionset forth in the instant invention. See for example, the results labeled64 on FIG. 9. Equation [2] has been found to be less than 50% efficient,needing more than 1 kg of reactants to obtain the same quantity of heatas provided by 100 g of Mg according to Equation [1]. The heat generatedaccording to Equation [1] is shown in the results labeled 66 on FIG. 9.Thus, when proceeding according to Equation [2], an additive, such ascarbon, is required in order to obtain a quantity of heat which issimilar to the heat produced via the reaction of Equation [1]. Thiseffect is shown in the results labeled 68 in the graph set forth in FIG.9.

As described above, reactions of Mg+MnO₂ with water can proceed viaeither Equation [1] and/or Equation [2] to provide heat. The reactionwhich dominates the generation of heat can be determined by measuringthe amount of hydrogen generated during the course of the reaction usingthe setup shown in FIG. 10. The reaction mixture of Mg+MnO₂ with waterproceeds in double necked round bottom flask 100, e.g., a 250 ml doublenecked round bottom flask. Temperature measurements are obtained byplacing a thermocouple within the reaction mixture via opening 102, forexample, and the data is gathered manually or via a data acquisitionsystem, e.g., Fluke Hydra data acquisition program interfaced with acomputer. Gases generated during the reaction passes from flask 100 toinverted graduated cylinder 104 via connection 106. Cylinder 104 isfilled with water and placed within reservoir 108 as shown in the FIG.10. Reservoir 108 is filled with water 110 whereby the water ismaintained in cylinder 104 until such time as gases pass from flask 100to cylinder 104. As gases are introduced to cylinder 104, watercontained therein is displaced. The amount of hydrogen generated by thereaction is calculated from the volume and composition of gases in flask100 and cylinder 104. Table 2 below shows the data gathered for severalexamples reaction mixtures.

TABLE 2 Maximum % Hydrogen System Temperature (° C.) generated¹ Mg + H₂O60 100 Mg + MnO₂ + H₂O 30 15 Mg + MnO₂ + C + H₂O 60 50 ¹Percent hydrogenevolved compared to percent hydrogen expected if all the Mg had directlyreacted with H₂O

It has been found, according to the data set forth in Table 2, that thereaction mixture which includes Mg+MnO₂ does proceed as dictated bythermodynamics, but not at a rate that is needed to heat rations with acomparable weight of Mg. Therefore, the temperature has not reached adesirable value, e.g., 60° C. However, even under these conditions, areaction according to Equation [1] is occurring, as evidenced by theamount of H₂ generated. It has been further found that when carbon isincluded in the reaction mixture, i.e., Mg+MnO₂+C, heat is produced as aresult of the reactions set forth in both Equations [1] and [2]. This isevidenced by the amount of H₂ produced. The reaction of Equation [1] isa parallel reaction occurring during the course of the reaction ofEquation [2]. It is believed that the reaction of Equation [1] can besuppressed by: a) blocking the Mg reaction sites thereby preventing thereaction of Mg with water from the bulk; and/or, b) consuming thehydrogen as it is formed. The foregoing means for suppressing thereaction of Equation [1] are discussed here below.

The Mg reaction sites can be blocked by forming insoluble Mg species onthe Mg sites as the reaction of Mg with water is initiated. Theindividual steps involved in the reaction of Equation [1] are asfollows:

Mg→Mg²⁺+2e   [3]

2H₂O+2e→H₂+2OH⁻  [4]

The insoluble species of Mg include but are not limited to magnesiumsilicate, magnesium bicarbonate, magnesium phosphate, magnesium borate,magnesium perborate, magnesium percarbonate, magnesium perphosphate andmagnesium persulfate. Thus, when sodium salts of anions such assilicate, carbonate, bicarbonate, phosphate, borate, perborate,percarbonate, perphosphate and persulfate (individually or incombination) are added to the Mg+MnO₂+C mixtures, these anions combinewith Mg²⁺ formed via Equation [3] to form insoluble Mg compounds on Mgreaction sites. As a result, the reaction of Equation [3] is pushed inthe reverse direction, which in turn suppresses the reaction of Equation[4]. Since the reaction of Equation [1] is suppressed, the reaction ofEquation [2] proceeds without hindrance, since the reaction of Equation[2] is a surface reaction. It should be noted that Equation [2] is anelectrochemical corrosion reaction wherein the anodic reaction is theoxidation of Mg to form Mg²⁺ ions, the cathodic reaction is thereduction of MnO₂ to Mn₂O₃ and the electron transfer processes proceedon the surface of MnO₂. It should be emphasized that alkali and alkalineearth salts with anions such as chloride, bromide, fluoride, hydroxide,acetate, citrate, etc., will not suppress the hydrogen evolutionreaction because they do not form insoluble films of Mg on the Mgsurfaces. The foregoing sodium salts may be added to the presentinvention composition as an activating solution/fluid, or alternatively,the salts may be added to the composition as a dry component, whereinthe salts dissolve upon the introduction of water to the composition.Moreover, the sodium salts may be added individually or as a combinationof a plurality of salts.

Example 21

A 99.98% pure magnesium powder of 200-300μ particle size from SuperiorMetal Powders and containing 60 ppm Al, 50 ppm Cu, 300 ppm Fe, 700 ppmMn, 50 ppm Si, 50 ppm Zn and 80 ppm Sn was used in this example. The70-80μ γ-MnO₂ was from Tronox, LLC with a purity of 99% and contained1.2% 50₄ ²⁻, 2600 ppm Na, 190 ppm Al, 310 ppm C, 35 ppm Fe and 400 ppmK. These two materials were used to make a batch sample, in astoichiometric ratio according to Equation [1] along with 5% Asbury 4827carbon, a synthetic graphite of <20-<30μ particle size, containing 1440ppm Al, 865 ppm Ca, 2150 ppm Fe, 2900 ppm Si, 300 ppm Mg, 200 ppm Na and2900 ppm Si.

Approximately 1100 g of the mixture containing 919.2 g MnO₂, 52.2 g C,130 g Mg was weighed and placed in the Vibrokinetic Energy (VKE) Mill,from Microgrinding System, Inc., Model 624 (diameter=6″ and tubelength=24″). This mill ran using 36 stainless steel rods (6 with adiameter=1″, 30 with a diameter= 7/16″) with a length of 24″ as astainless steel rod. The sample mixture was loaded into the mill via the2″ diameter feed. All the screws and openings were tightened and securedprior to running the mill for 1.5 hours. At the end of 1.5 hours, thesample was left in the mill for 20 minutes to cool. The sample wasremoved with a Nalgene scoop, transferred to a 1000 ml stainless steelbeaker and stored in a desiccator with calcium sulfate as thedehydrating agent.

A composite Unilayer 135/Unipro-SMS bag material from Midwest filtrationwas used to contain the milled Mg/MnO₂/C mixture. First, the bagmaterial was cut into a 16.5″×11″ sheet and folded in half to make a8.25″×11″ bag. Prior to adding the sample, one of the 8.25″ sides andthe 11″ side is heat sealed to form a pocket. The task was done with aUline 8″ impulse Sealer (Model H-163). 450 g of the milled Mg/MnO₂/C wasplaced in the Unilayer Pocket and sealed closed. This completed rationheater was placed in a UGR-E tray, over which a 3500 g “water pouch” wasplaced. This assembly was placed in a card board box and then 350 ml of2.3% sodium silicate water was added. The card board box was then closedand the edges sealed with a tape. The temperature variation was recordedas a function of time over a 60 minute period, and presented in FIG. 11.The results labeled 120 depict the performance of a mixture of Mg/Feactivated by 330 ml NaCl, while the results labeled 122 depict theperformance of a mixture of Mg/MnO₂/C activated by 330 ml of 2.3% sodiumsilicate solution.

An analysis of the gases produced, following the methodology describedearlier, showed the percent hydrogen evolved compared to that expectedif all the Mg has directly reacted with H₂O to be ˜10%. This translatesto approximately a 95% reduction in the amount of hydrogen generatedwhen compared to a 110 g Mg/Fe heater that is presently used in UGR-Eheaters.

Moreover, the hydrogen from the foregoing reactions can be consumed asit is formed. An alternate approach to suppress hydrogen generation isto react it as it is formed by oxidizing it to form protons as:

H₂+2e→2H⁻  [5]

This scheme requires the presence of species that can be reduced. Thereducible species are cations such as Cu²⁺, Ni²⁺ or anions such asnitrate, nitrite, ferrate, permanganate, and stannate. Cu²⁺, Ni²⁺ willbe reduced to metallic Cu or Ni, which are carcinogenic and cannot comein contact with food products. The reducible species with perborate andpercarbonate additions is H₂O₂ formed by the hydrolysis of thesespecies. Tests have shown that nitrate and nitrite completely suppressH₂ generation, but the reduced product in both cases is ammonia whichsmells and hence is not acceptable with food products. Permanganate andferrate are reduced to MnO₂ and Fe³⁺, respectively. These species arecolored and hence stain the bag material and the bottom of the foodtray. While these suppressants can be used to prevent hydrogenevolution, they are not preferred because of aesthetic aspects,especially with foods and food products.

Example 22

This example comprises a comparison of a variety of compositionsincluding the instant invention and several known compositions. Thefirst composition includes: 4 g of a Mg/Fe mixture, 40.25 g of CuCl₂(which is equivalent to 51 g of CuCl₂.2H₂O), 7.7 g of Citric acid and34.2 g of sodium citrate which equals 86.15 g of total composition. Thiscomposition is Example 1 from U.S. Pat. No. 5,517,981 (hereinafterTaub). The second, third and fourth compositions each includes: 1.56 gof Mg, 11.18 g of MnO₂ and 2.25 g of carbon.

The first composition was activated with 11 mL of water, the secondcomposition was activated with 11 mL of water having 1.5% NaCl, thethird composition was activated with 11 mL of water and the fourthcomposition was activated with 11 mL of water having 2.3% sodiumsilicate. FIG. 12 shows the temperature versus time for each of thecompositions. Line 124 shows the results of the first composition, line126 shows the results of the second composition, line 128 shows theresults of the third composition and line 130 shows the results of thefourth composition. The following table sets forth the performance ofeach composition.

TABLE 3 H₂ (calculated H₂ Expected (based based on volume Activation onMg reaction measurements) Composition¹ System Solution² with H₂O) (mL)(mL) First Taub Example 1 H₂O 670 100 Second Mg/MnO₂/15% C 1.5% NaCl1440 910 Third Mg/MnO₂/15% C H₂O 1440 540 Fourth Mg/MnO₂/15% C 2.3%Na₂SiO₃ 1440 180 ¹All compositions used as 15 g samples ²All activationsolutions include 11 mL of H₂O

It should be appreciated that the reaction of Taub provides heataccording to the reaction of Equation [6].

Mg+CuCl₂→MgCl₂+Cu   [6]

The reaction of Equation [6] has a heat of reaction of 101 kcal/moleverses 85.88 kcal/mole for the reaction of Equation [1]. Moreover, theTaub reaction produces metallic Cu fines which block the cloth bag whichhouses the reaction mixture thereby preventing steam from getting out ofthe bag and which in turn heat the water pouch. As the water pouch isheavy, i.e., weighing approximately 3.5 kg, the steam was prevented fromescaping to heat the water. Once the water pouch was removed, the bagexpanded as the steam was not able to get out. Furthermore, the Taubcomposition developed blackish green color as the reaction proceededmaking the heater bag appear undesirable. Lastly, the Taub compositionresults in Cu which is a known carcinogenic material and hence notpermitted near food.

Lastly, it should be noted that the nature of the wetting agent employedto impart hydrophilicity to a given polymeric filter media and themanner in which it is applied impacts the temperature-time profile andthe fines retention characteristics of the composite bag materials forhousing the heater chemicals. Pluronic 25R2, a BASF product, which is apolyoxypropylene-polyoxypolyethylene block copolymer is generally usedto wet polyester media. Eccowet D-75B, a product of Eastern Color &Chemical Company, which is a sodium sulfo-succinate solution inpropylene glycol is used for polypropylene based media. It has beenfound that a proper wetting agent should be used for a given polymericmaterial, as otherwise, the heat generation profiles will besignificantly altered.

Tests have also shown that the manner by which the wetting agents areapplied to a given material makes a difference in the temperatureprofiles and the appearance of the heater bag after use. Pluronic isapplied by lightly dabbing it on the bag with a brush or adding measurednumber of drops in select locations on the heater bag, whereas Eccowetis impregnated on the cloth by soaking it in a 1-5% solution of thewetting agent, squeezing the excess solution and drying it at 90-100° C.The procedure used for Eccowet is not applicable with Pluronic, sincethis leads to lowered temperature profiles and unacceptable seepage ofblack fines.

While the invention has been described in conjunction with variousembodiments, they are illustrative only. Accordingly, many alternatives,modifications and variations will be apparent to persons skilled in theart in light of the foregoing detailed description, and it is thereforeintended to embrace all such alternatives and variations as to fallwithin the spirit and broad scope of the appended claims.

1. A method for generating energy for flameless heating, which comprisesthe steps of: (i) forming a reaction mixture comprising magnesium ormagnesium-containing alloy, a hydrogen eliminator or suppressor andparticulate carbon; and, (ii) adding a metallic salt and water to saidreaction mixture, said metallic salt comprises a cation and an anion andsaid anion is selected from the group consisting of silicate, carbonate,bicarbonate, phosphate, borate, perborate, percarbonate, perphosphate,persulfate, nitrate, nitrite, ferrate, permanganate, and stannate andcombinations thereof, wherein the metallic salt and water are addedeither sequentially or together and wherein said reaction mixture,metallic salt and water in combination generate sufficient thermalenergy for heating an article or substance while simultaneouslyeliminating or suppressing the generation of hydrogen.
 2. The methodaccording to claim 1, wherein the hydrogen suppressor is a transitionmetal oxide.
 3. The method according to claim 2, wherein the transitionmetal oxide is an oxide of manganese or ruthenium.
 4. The methodaccording to claim 1, wherein the magnesium-containing alloy comprisesat least one alloying element selected from the group consisting ofiron, cobalt, nickel, zinc, aluminum and mixtures thereof.
 5. The methodaccording to claim 1, wherein the reaction mixture (i) further comprisesat least one member selected from the group consisting of a hydrogenovervoltage suppressor, a flowing agent and a reaction activator.
 6. Themethod according to claim 5, wherein the hydrogen overvoltage suppressoris a metal sulfide; said flowing agent is silica or calcium carbonate;and, the reaction activator is a salt selected from the group consistingof sodium halide, magnesium halide and magnesium perchlorate.
 7. Themethod according to claim 5, wherein said reaction mixture (i) is formedby milling said magnesium or magnesium-containing alloy, said hydrogeneliminator or suppressor and particulate carbon, and mixing said milledreaction mixture with said at least one member selected from the groupconsisting of said hydrogen overvoltage suppressor, said flowing agent,said metallic salt and said reaction activator prior to activating theheater reaction with water.
 8. The method according to claim 1, whereinsaid cation is selected from the group consisting of an alkaline metaland an alkali metal.
 9. The method according to claim 1, wherein saidcation is selected from the group consisting of calcium, magnesium andpotassium.
 10. A hydrogen suppressing, flameless, heat generatingchemical composition comprising: magnesium or a magnesium-containingalloy; a hydrogen suppressor or eliminator; particulate carbon; ametallic salt comprising a cation and an anion, wherein said anion isselected from the group consisting of silicate, carbonate, bicarbonate,phosphate, borate, perborate, percarbonate, perphosphate, persulfate,nitrate, nitrite, ferrate, permanganate, and stannate and combinationsthereof; and, water, wherein said magnesium or magnesium-containingalloy, hydrogen suppressor or eliminator, particulate carbon, metallicsalt and water are each present in a proportional amount to generatesufficient heat to heat water, medical supplies and/or consumablerations.
 11. The hydrogen suppressing, flameless, heat generatingchemical composition according to claim 10, further comprising at leastone member selected from the group consisting of a hydrogen overvoltagesuppressor, a flowing agent and a reaction activator.
 12. The hydrogensuppressing, flameless, heat generating chemical composition accordingto claim 10, wherein said magnesium-containing alloy comprises at leastone alloying member selected from the group consisting of iron, cobalt,nickel, zinc, aluminum and mixtures thereof.
 13. The hydrogensuppressing, flameless, heat generating chemical composition accordingto claim 10, wherein said hydrogen suppressor comprises oxides ofmanganese and/or ruthenium.
 14. The hydrogen suppressing, flameless,heat generating chemical composition according to claim 13, wherein saidoxide of manganese is γ-MnO₂ or β-MnO₂.
 15. The hydrogen suppressing,flameless, heat generating chemical composition according to claim 13,wherein the oxide of manganese is present in an amount ranging from 0.5to about 10 times the stoichiometric amount required for the magnesiumand the oxide of manganese reaction with water to occur.
 16. Thehydrogen suppressing, flameless, heat generating chemical compositionaccording to claim 11, wherein the hydrogen overvoltage suppressor is ametal sulfide and the activator is an inorganic salt.
 17. The hydrogensuppressing, flameless, heat generating composition according to claim11, wherein the reaction activator is magnesium chloride present in anamount from about 0.001 to about 50 percent by-weight.
 18. The hydrogensuppressing, flameless, heat generating composition according to claim17, wherein the reaction activator is mixed with milledmagnesium-manganese dioxide mixtures prior to activating the heaterreaction with water.
 19. The hydrogen suppressing, flameless, heatgenerating composition according to claim 11, wherein the reactionactivator is a thermally and electrically conducting, high surface areasynthetic graphite present in an amount from about 0.001 to about 50percent by-weight.
 20. The hydrogen suppressing, flameless, heatgenerating composition according to claim 19, wherein the syntheticgraphite is Asbury
 4827. 21. The hydrogen suppressing, flameless, heatgenerating composition according to claim 11, wherein the reactionactivator is a conducting carbon present in an amount from about 0.001to about 50 percent by-weight.
 22. The hydrogen suppressing, flameless,heat generating composition according to claim 21, wherein theconducting carbon is Ketjenblack, Black Pearls® 2000, Black Pearls® 1300or Asbury TC
 307. 23. The hydrogen suppressing, flameless, heatgenerating composition according to claim 11, wherein the reactionactivator is a conducting graphite or carbon present in an amount fromabout 0.001 to about 50 percent by-weight and the reaction activator ismixed with a magnesium-manganese dioxide mixture in a vibratory or ballmill for at least an hour.
 24. The hydrogen suppressing, flameless, heatgenerating composition according to claim 10, wherein said cation isselected from the group consisting of an alkaline metal and an alkalimetal.
 25. The hydrogen suppressing, flameless, heat generatingcomposition according to claim 10, wherein said cation is selected fromthe group consisting of calcium, magnesium and potassium.
 26. Thehydrogen suppressing, flameless, heat generating composition accordingto claim 10, wherein the metallic salt and water are added eithersequentially or together.
 27. A heater device comprising the hydrogensuppressing, flameless, heat generating chemical composition accordingto claim
 10. 28. The heater device of claim 27 wherein the hydrogensuppressing, flameless, heat generating chemical composition is enclosedwithin a bag comprising a filter cloth, wherein said filter clothcomprises a 6-ply sonic bonded polypropylene laminate.
 29. The heaterdevice of claim 27 wherein the hydrogen suppressing, flameless, heat ingenerating chemical composition is enclosed within a dual layer bagcomprising a first layer comprising polyester fibers and a second layercomprising polypropylene fibers.
 30. The heater device of claim 27wherein the hydrogen suppressing, flameless, heat generating chemicalcomposition is enclosed within a multi-layer bag comprising a pluralityof layers of polyester fibers.
 31. The heater device of claim 27 whereinthe hydrogen suppressing, flameless, heat generating chemicalcomposition is enclosed within a dual layer bag comprising an outerlayer of 3-ply bonded polypropylene fiber cloth and an inner layer ofspunbond/meltblown/spunbond filter media comprising polypropylene.
 32. Ameal, ready-to-eat package comprising the flameless heater deviceaccording to claim 27.